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@Article { GatysETB2015_2,
title = {Synaptic unreliability facilitates information transmission in balanced cortical populations},
journal = {Physical Review E},
year = {2015},
month = {6},
volume = {91},
number = {062707},
pages = {1-7},
abstract = {Synaptic unreliability is one of the major sources of biophysical noise in the brain. In the context of neural information processing, it is a central question how neural systems can afford this unreliability. Here we examine how synaptic noise affects signal transmission in cortical circuits, where excitation and inhibition are thought to be tightly balanced. Surprisingly, we find that in this balanced state synaptic response variability actually facilitates information transmission, rather than impairing it. In particular, the transmission of fast-varying signals benefits from synaptic noise, as it instantaneously increases the amount of information shared between presynaptic signal and postsynaptic current. Furthermore we show that the beneficial effect of noise is based on a very general mechanism which contrary to stochastic resonance does not reach an optimum at a finite noise level.
PDFHTML},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://journals.aps.org/pre/pdf/10.1103/PhysRevE.91.062707},
DOI = {10.1103/PhysRevE.91.062707},
author = {Gatys, LA and Ecker, AS and Tchumatchenko, T and Bethge, M}
}
@Article { GatysEB2015,
title = {Texture synthesis and the controlled generation of natural stimuli using convolutional neural networks},
journal = {-},
year = {2015},
month = {5},
pages = {1-9},
abstract = {It is a long standing question how biological systems transform visual inputs to robustly infer high-level visual information. Research in the last decades has established that much of the underlying computations take place in a hierarchical fashion along the ventral visual pathway. However, the exact processing stages along this hierarchy are difficult to characterise. Here we present a method to generate stimuli that will allow a principled description of the processing stages along the ventral stream. We introduce a new parametric texture model based on the powerful feature spaces of convolutional neural networks optimised for object recognition. We show that constraining a spatial summary statistic over feature maps suffices to synthesise high-quality natural textures. Moreover we establish that our texture representations continuously disentangle high-level visual information and demonstrate that the hierarchical parameterisation of the texture model naturally enables us to generate novel types of stimuli for systematically probing mid-level vision.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
web_url = {http://arxiv.org/abs/1505.07376},
state = {submitted},
author = {Gatys, LA and Ecker, AS and Bethge, M}
}
@Article { YatsenkoJEFCT2015,
title = {Improved Estimation and Interpretation of Correlations in Neural Circuits},
journal = {PLoS Computational Biology},
year = {2015},
month = {3},
volume = {11},
number = {3},
pages = {1-28},
abstract = {Ambitious projects aim to record the activity of ever larger and denser neuronal populations in vivo. Correlations in neural activity measured in such recordings can reveal important aspects of neural circuit organization. However, estimating and interpreting large correlation matrices is statistically challenging. Estimation can be improved by regularization, i.e. by imposing a structure on the estimate. The amount of improvement depends on how closely the assumed structure represents dependencies in the data. Therefore, the selection of the most efficient correlation matrix estimator for a given neural circuit must be determined empirically. Importantly, the identity and structure of the most efficient estimator informs about the types of dominant dependencies governing the system. We sought statistically efficient estimators of neural correlation matrices in recordings from large, dense groups of cortical neurons. Using fast 3D random-access laser scanning microscopy of calcium signals, we recorded the activity of nearly every neuron in volumes 200 \(\mu\)m wide and 100 \(\mu\)m deep (150–350 cells) in mouse visual cortex. We hypothesized that in these densely sampled recordings, the correlation matrix should be best modeled as the combination of a sparse graph of pairwise partial correlations representing local interactions and a low-rank component representing common fluctuations and external inputs. Indeed, in cross-validation tests, the covariance matrix estimator with this structure consistently outperformed other regularized estimators. The sparse component of the estimate defined a graph of interactions. These interactions reflected the physical distances and orientation tuning properties of cells: The density of positive ‘excitatory’ interactions decreased rapidly with geometric distances and with differences in orientation preference whereas negative ‘inhibitory’ interactions were less selective. Because of its superior performance, this ‘sparse+latent’ estimator likely provides a more physiologically relevant representation of the functional connectivity in densely sampled recordings than the sample correlation matrix.},
department = {Department Logothetis},
web_url = {http://www.ploscompbiol.org/article/fetchObject.action?uri=info:doi/10.1371/journal.pcbi.1004083\&representation=PDF},
DOI = {10.1371/journal.pcbi.1004083},
EPUB = {e1004083},
author = {Yatsenko, D and Josić, K and Ecker, AS and Froudarakis, E and Cotton, RJ and Tolias, AS}
}
@Article { EckerT2014,
title = {Is there signal in the noise?},
journal = {Nature Neuroscience},
year = {2014},
month = {6},
volume = {17},
number = {6},
pages = {750-751},
abstract = {A study now shows that variability in neuronal responses in the visual system mainly arises from slow fluctuations in excitability, presumably caused by factors of nonsensory origin, such as arousal, attention or anesthesia.},
department = {Department Logothetis},
web_url = {http://www.nature.com/neuro/journal/v17/n6/pdf/nn.3722.pdf},
DOI = {10.1038/nn.3722},
author = {Ecker, AS and Tolias, AS}
}
@Article { FroudarakisBECSYSBT2014,
title = {Population code in mouse V1 facilitates readout of natural scenes through increased sparseness},
journal = {Nature Neuroscience},
year = {2014},
month = {6},
volume = {17},
number = {6},
pages = {851–857},
abstract = {Neural codes are believed to have adapted to the statistical properties of the natural environment. However, the principles that govern the organization of ensemble activity in the visual cortex during natural visual input are unknown. We recorded populations of up to 500 neurons in the mouse primary visual cortex and characterized the structure of their activity, comparing responses to natural movies with those to control stimuli. We found that higher order correlations in natural scenes induced a sparser code, in which information is encoded by reliable activation of a smaller set of neurons and can be read out more easily. This computationally advantageous encoding for natural scenes was state-dependent and apparent only in anesthetized and active awake animals, but not during quiet wakefulness. Our results argue for a functional benefit of sparsification that could be a general principle governing the structure of the population activity throughout cortical microcircuits.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
department3 = {Department Sch{\"o}lkopf},
web_url = {http://www.nature.com/neuro/journal/v17/n6/pdf/nn.3707.pdf},
DOI = {10.1038/nn.3707},
author = {Froudarakis, E and Berens, P and Ecker, AS and Cotton, RJ and Sinz, FH and Yatsenko, D and Saggau, P and Bethge, M and Tolias, AS}
}
@Article { EckerBCSDCSBT2014,
title = {State Dependence of Noise Correlations in Macaque Primary Visual Cortex},
journal = {Neuron},
year = {2014},
month = {4},
volume = {82},
number = {1},
pages = {235–248},
abstract = {Shared, trial-to-trial variability in neuronal populations has a strong impact on the accuracy of information processing in the brain. Estimates of the level of such noise correlations are diverse, ranging from 0.01 to 0.4, with little consensus on which factors account for these differences. Here we addressed one important factor that varied across studies, asking how anesthesia affects the population activity structure in macaque primary visual cortex. We found that under opioid anesthesia, activity was dominated by strong coordinated fluctuations on a timescale of 1–2 Hz, which were mostly absent in awake, fixating monkeys. Accounting for these global fluctuations markedly reduced correlations under anesthesia, matching those observed during wakefulness and reconciling earlier studies conducted under anesthesia and in awake animals. Our results show that internal signals, such as brain state transitions under anesthesia, can induce noise correlations but can also be estimated and accounted for based on neuronal population activity.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
department3 = {Department Sch{\"o}lkopf},
web_url = {http://www.sciencedirect.com/science/article/pii/S0896627314001044},
DOI = {10.1016/j.neuron.2014.02.006},
author = {Ecker, AS and Berens, P and Cotton, RJ and Subramaniyan, M and Denfield, GH and Cadwell, CR and Smirnakis, SM and Bethge, M and Tolias, AS}
}
@Article { SubramaniyanEBT2013,
title = {Macaque Monkeys Perceive the Flash Lag Illusion},
journal = {PLoS ONE},
year = {2013},
month = {3},
volume = {8},
number = {3},
pages = {1-10},
abstract = {Transmission of neural signals in the brain takes time due to the slow biological mechanisms that mediate it. During such delays, the position of moving objects can change substantially. The brain could use statistical regularities in the natural world to compensate neural delays and represent moving stimuli closer to real time. This possibility has been explored in the context of the flash lag illusion, where a briefly flashed stimulus in alignment with a moving one appears to lag behind the moving stimulus. Despite numerous psychophysical studies, the neural mechanisms underlying the flash lag illusion remain poorly understood, partly because it has never been studied electrophysiologically in behaving animals. Macaques are a prime model for such studies, but it is unknown if they perceive the illusion. By training monkeys to report their percepts unbiased by reward, we show that they indeed perceive the illusion qualitatively similar to humans. Importantly, the magnitude of the illusion is smaller in monkeys than in humans, but it increases linearly with the speed of the moving stimulus in both species. These results provide further evidence for the similarity of sensory information processing in macaques and humans and pave the way for detailed neurophysiological investigations of the flash lag illusion in behaving macaques.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
web_url = {http://www.plosone.org/article/fetchObject.action?uri=info\%3Adoi\%2F10.1371\%2Fjournal.pone.0058788\&representation=PDF},
DOI = {10.1371/journal.pone.0058788},
EPUB = {e58788},
author = {Subramaniyan, M and Ecker, AS and Berens, P and Tolias, AS}
}
@Article { BerensECMBT2012,
title = {A Fast and Simple Population Code for Orientation in Primate V1},
journal = {Journal of Neuroscience},
year = {2012},
month = {8},
volume = {32},
number = {31},
pages = {10618-10626},
abstract = {Orientation tuning has been a classic model for understanding single-neuron computation in the neocortex. However, little is known about how orientation can be read out from the activity of neural populations, in particular in alert animals. Our study is a first step toward that goal. We recorded from up to 20 well isolated single neurons in the primary visual cortex of alert macaques simultaneously and applied a simple, neurally plausible decoder to read out the population code. We focus on two questions: First, what are the time course and the timescale at which orientation can be read out from the population response? Second, how complex does the decoding mechanism in a downstream neuron have to be to reliably discriminate between visual stimuli with different orientations? We show that the neural ensembles in primary visual cortex of awake macaques represent orientation in a way that facilitates a fast and simple readout mechanism: With an average latency of 30–80 ms, the population code can be read out instantaneously with a short integration time of only tens of milliseconds, and neither stimulus contrast nor correlations need to be taken into account to compute the optimal synaptic weight pattern. Our study shows that—similar to the case of single-neuron computation—the representation of orientation in the spike patterns of neural populations can serve as an exemplary case for understanding the computations performed by neural ensembles underlying visual processing during behavior.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
department3 = {Department Sch{\"o}lkopf},
web_url = {http://www.jneurosci.org/content/32/31/10618.full.pdf+html},
DOI = {10.1523/​JNEUROSCI.1335-12.2012},
author = {Berens, P and Ecker, AS and Cotton, RJ and Ma, WJ and Bethge, M and Tolias, AS}
}
@Article { EckerBTB2011,
title = {The effect of noise correlations in populations of diversely tuned neurons},
journal = {Journal of Neuroscience},
year = {2011},
month = {10},
volume = {31},
number = {40},
pages = {14272-14283},
abstract = {The amount of information encoded by networks of neurons critically depends on the correlation structure of their activity. Neurons with similar stimulus preferences tend to have higher noise correlations than others. In homogeneous populations of neurons, this limited range correlation structure is highly detrimental to the accuracy of a population code. Therefore, reduced spike count correlations under attention, after adaptation, or after learning have been interpreted as evidence for a more efficient population code. Here, we analyze the role of limited range correlations in more realistic, heterogeneous population models. We use Fisher information and maximum-likelihood decoding to show that reduced correlations do not necessarily improve encoding accuracy. In fact, in populations with more than a few hundred neurons, increasing the level of limited range correlations can substantially improve encoding accuracy. We found that this improvement results from a decrease in noise entropy that is associated with increasing correlations if the marginal distributions are unchanged. Surprisingly, for constant noise entropy and in the limit of large populations, the encoding accuracy is independent of both structure and magnitude of noise correlations.},
department = {Department Sch{\"o}lkopf},
department2 = {Research Group Bethge},
department3 = {Department Logothetis},
web_url = {http://www.jneurosci.org/content/31/40/14272.full.pdf+html},
DOI = {10.1523/​JNEUROSCI.2539-11.2011},
author = {Ecker, AS and Berens, P and Tolias, AS and Bethge, M}
}
@Article { BerensEGTB2011,
title = {Reassessing optimal neural population codes with neurometric functions},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
year = {2011},
month = {3},
volume = {108},
number = {11},
pages = {4423-4428},
abstract = {Cortical circuits perform the computations underlying rapid perceptual decisions within a few dozen milliseconds with each neuron emitting only a few spikes. Under these conditions, the theoretical analysis of neural population codes is challenging, as the most commonly used theoretical tool—Fisher information—can lead to erroneous conclusions about the optimality of different coding schemes. Here we revisit the effect of tuning function width and correlation structure on neural population codes based on ideal observer analysis in both a discrimination and a reconstruction task. We show that the optimal tuning function width and the optimal correlation structure in both paradigms strongly depend on the available decoding time in a very similar way. In contrast, population codes optimized for Fisher information do not depend on decoding time and are severely suboptimal when only few spikes are available. In addition, we use the neurometric functions of the ideal observer in the classification task to investigate the differential coding properties of these Fisher-optimal codes for fine and coarse discrimination. We find that the discrimination error for these codes does not decrease to zero with increasing population size, even in simple coarse discrimination tasks. Our results suggest that quite different population codes may be optimal for rapid decoding in cortical computations than those inferred from the optimization of Fisher information.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
web_url = {http://www.pnas.org/content/108/11/4423.full.pdf+html},
DOI = {10.1073/pnas.1015904108},
author = {Berens, P and Ecker, AS and Gerwinn, S and Tolias, AS and Bethge, M}
}
@Article { 6257,
title = {Decorrelated Neuronal Firing in Cortical Microcircuits},
journal = {Science},
year = {2010},
month = {1},
volume = {327},
number = {5965},
pages = {584-587},
abstract = {Correlated trial-to-trial variability in the activity of cortical neurons is thought to reflect the functional connectivity of the circuit. Many cortical areas are organized into functional columns, in which neurons are believed to be densely connected and to share common input. Numerous studies report a high degree of correlated variability between nearby cells. We developed chronically implanted multitetrode arrays offering unprecedented recording quality to reexamine this question in the primary visual cortex of awake macaques. We found that even nearby neurons with similar orientation tuning show virtually no correlated variability. Our findings suggest a refinement of current models of cortical microcircuit architecture and function: Either adjacent neurons share only a few percent of their inputs or, alternatively, their activity is actively decorrelated.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://www.sciencemag.org/cgi/reprint/327/5965/584.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1126/science.1179867},
author = {Ecker, AS and Berens, P and Keliris, GA and Bethge, M and Logothetis, NK and Tolias, AS}
}
@Article { 5157,
title = {Generating Spike Trains with Specified Correlation Coefficients},
journal = {Neural Computation},
year = {2009},
month = {2},
volume = {21},
number = {2},
pages = {397-423},
abstract = {Spike trains recorded from populations of neurons can exhibit substantial pairwise correlations between neurons and rich temporal structure. Thus, for the realistic simulation and analysis of neural systems, it is essential to have efficient methods for generating artificial spike trains with specified correlation structure. Here we show how correlated binary spike trains can be simulated by means of a latent multivariate gaussian model. Sampling from the model is computationally very efficient and, in particular, feasible even for large populations of neurons. The entropy of the model is close to the theoretical maximum for a wide range of parameters. In addition, this framework naturally extends to correlations over time and offers an elegant way to model correlated neural spike counts with arbitrary marginal distributions.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/macke2009_5157[0].pdf},
department = {Department Sch{\"o}lkopf},
department2 = {Research Group Bethge},
web_url = {http://www.mitpressjournals.org/doi/pdf/10.1162/neco.2008.02-08-713},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1162/neco.2008.02-08-713},
author = {Macke, JH and Berens, P and Ecker, AS and Tolias, AS and Bethge, M}
}
@Article { 5614,
title = {Feature selectivity of the gamma-band of the local field potential in primate primary visual cortex},
journal = {Frontiers in Neuroscience},
year = {2008},
month = {12},
volume = {2},
number = {2},
pages = {199-207},
abstract = {Extra-cellular voltage fluctuations (local field potentials; LFPs) reflecting neural mass action are ubiquitous across species and brain regions. Numerous studies have characterized the properties of LFP signals in the cortex to study sensory and motor computations as well as cognitive processes like attention, perception and memory. In addition, its extracranial counterpart  the electroencelphalogram (EEG)  is widely used in clinical applications. However, the link between LFP signals and the underlying activity of local populations of neurons remains largely elusive. Here, we review recent work elucidating the relationship between spiking activity of local neural populations and LFP signals. We focus on oscillations in the gamma-band (30-90Hz) of the local field potential in the primary visual cortex (V1) of the macaque that dominate during visual stimulation. Given that in area V1 much is known about the properties of single neurons and the cortical architecture, it provides an excellent opportunity to
study the mechanisms underlying the generation of the local field potential.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://frontiersin.org/neuroscience/paper/10.3389/neuro.01/037.2008/pdf/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.3389/neuro.01.037.2008},
author = {Berens, P and Keliris, GA and Ecker, AS and Logothetis, NK and Tolias, AS}
}
@Article { 5205,
title = {Comparing the feature selectivity of the gamma-band of the local field potential and the underlying spiking activity in primate visual cortex},
journal = {Frontiers in Systems Neuroscience},
year = {2008},
month = {6},
volume = {2},
number = {2},
pages = {1-11},
abstract = {The local field potential (LFP), comprised of low-frequency extra-cellular voltage fluctuations, has been used extensively to study the mechanisms of brain function. In particular, oscillations in the gamma-band (3090 Hz) are ubiquitous in the cortex of many species during various cognitive processes. Surprisingly little is known about the underlying biophysical processes generating this signal. Here, we examine the relationship of the local field potential to the activity of localized populations of neurons by simultaneously recording spiking activity and LFP from the primary visual cortex (V1) of awake, behaving macaques. The spatial organization of orientation tuning and ocular dominance in this area provides an excellent opportunity to study this question, because orientation tuning is organized at a scale around one order of magnitude finer than the size of ocular dominance columns. While we find a surprisingly weak correlation between the preferred orientation of multi-unit activity and gamma-band LFP
recorded on the same tetrode, there is a strong correlation between the ocular preferences of both signals. Given the spatial arrangement of orientation tuning and ocular dominance, this leads us to conclude that the gamma-band of the LFP seems to sample an area considerably larger than orientation columns. Rather, its spatial resolution lies at the scale of ocular dominance columns.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://www.frontiersin.org/systemsneuroscience/paper/10.3389/neuro.06/002.2008/pdf/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.3389/neuro.06.002.2008},
author = {Berens, P and Keliris, GA and Ecker, AS and Logothetis, NK and Tolias, AS}
}
@Article { 4788,
title = {Recording Chronically from the same Neurons in Awake, Behaving Primates},
journal = {Journal of Neurophysiology},
year = {2007},
month = {12},
volume = {98},
number = {6},
pages = {3780-3790},
abstract = {Understanding the mechanisms of learning requires characterizing how the response properties of individual neurons and interactions across populations of neurons change over time. In order to study learning in-vivo, we need the ability to track an electrophysiological signature that uniquely identifies each recorded neuron for extended periods of time. We have identified such an extracellular signature using a statistical framework which allows quantification of the accuracy by which stable neurons can be identified across successive recording sessions. Our statistical framework uses spike waveform information recorded on a tetrodes four channels in order to define a measure of similarity between neurons recorded across time. We use this framework to quantitatively demonstrate for the first time the ability to record from the same neurons across multiple consecutive days and weeks. The chronic recording techniques and methods of analyses we report can be used to characterize the changes in brain circuits du
e to learning.},
department = {Department Logothetis},
web_url = {http://jn.physiology.org/cgi/reprint/00260.2007v1},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1152/jn.00260.2007},
author = {Tolias, AS and Ecker, AS and Siapas, AG and Hoenselaar, A and Keliris, GA and Logothetis, NK}
}
@Inproceedings { 6076,
title = {Neurometric function analysis of population codes},
journal = {Advances in Neural Information Processing Systems 22: 23rd Annual Conference on Neural Information Processing Systems 2009},
year = {2010},
month = {4},
pages = {90-98},
abstract = {The relative merits of different population coding schemes have mostly been analyzed in the framework of stimulus reconstruction using Fisher Information. Here, we consider the case of stimulus discrimination in a two alternative forced choice paradigm and compute neurometric functions in terms of the minimal discrimination error and the Jensen-Shannon information to study neural population codes.
We first explore the relationship between minimum discrimination error, Jensen-Shannon Information and Fisher Information and show that the discrimination framework is more informative about the coding accuracy than Fisher Information as it defines an error for any pair of possible stimuli. In particular, it includes Fisher Information as a special case. Second, we use the framework to study population codes of angular variables. Specifically, we assess the impact of different noise correlations structures on coding accuracy in long versus short decoding
time windows. That is, for long time window we use the common Gaussian noise approximation. To address the case of short time windows we analyze the Ising model with identical noise correlation structure. In this way, we provide a new rigorous framework for assessing the functional consequences of noise correlation structures for the representational accuracy of neural population codes that is in particular applicable to short-time population coding.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/berens2009b_6076[0].pdf},
department = {Research Group Bethge},
web_url = {http://nips.cc/Conferences/2009/},
editor = {Bengio, Y. , D. Schuurmans, J. Lafferty, C. Williams, A. Culotta},
publisher = {Curran},
address = {Red Hook, NY, USA},
booktitle = {Advances in Neural Information Processing Systems 22},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Vancouver, BC, Canada},
event_name = {23rd Annual Conference on Neural Information Processing Systems (NIPS 2009)},
language = {en},
ISBN = {978-1-615-67911-9},
author = {Berens, P and Gerwinn, S and Ecker, AS and Bethge, M}
}
@Poster { FroudarakisBECSYSBT2014_2,
title = {Population Code in Mouse V1 Facilities Read-out of Natural Scenes through Increased Sparseness},
year = {2014},
month = {6},
pages = {69},
abstract = {The neural code is believed to have adapted to the statistical properties of the natural environment.
However, the principles that govern the organization of ensemble activity in the visual cortex during natural visual input are unknown. We recorded populations of up to 500 neurons in the mouse primary visual cortex and characterized the structure of their activity, comparing
responses to natural movies with those to control stimuli. We found that higher-order correlations in natural scenes induce a sparser code, in which information is encoded by reliable activation of a smaller set of neurons and can be read-out more easily. This computationally advantageous encoding for natural scenes was state-dependent and apparent only in anesthetized and active, awake animals, but not during quiet wakefulness. Our results argue for a
functional benefit of sparsification that could be a general principle governing the structure of the population activity throughout cortical microcircuits.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://areadne.org/2014/home.html},
event_place = {Santorini, Greece},
event_name = {AREADNE 2014: Research in Encoding and Decoding of Neural Ensembles},
author = {Froudarakis, A and Berens, P and Ecker, AS and Cotton, RJ and Sinz, FH and Yatsenko, D and Saggau, P and Bethge, M and Tolias, AS}
}
@Poster { CottonFEBST2014,
title = {Scaling of Information in Large Sensory Neuronal Populations},
year = {2014},
month = {6},
pages = {60},
abstract = {Although we know a lot about how individual neurons in the brain represent the sensory environment, we are far from understanding how neural populations represent sensory information. Because individual neurons are noisy, pooling the activity of many neurons with similar response properties seems necessary to obtain an accurate representation of the sensory environment. However, it is widely believed that shared noise (or, noise correlations) in the activity of nearby neurons renders such pooling ineffective, profoundly limiting the accuracy of any
population code and, ultimately, behavior. This belief is based on model-based extrapolations from correlations measured in individual pairs of neurons, as it has been impossible to record simultaneously from complete neuronal populations. Here, we use a novel 3D high-speed in vivo two-photon microscope to record nearly all of the hundreds of neurons in a small volume of the mouse primary visual cortex and directly measure the amount of information encoded by these local populations. In contrast to previous predictions, we find that the information in a sensory population increases approximately linearly with population size and does not saturate even for several hundred neurons. Moreover, even a decoder ignoring correlations between neurons can decode 80\% of the information in the population. Our results suggest that sensory neural populations represent information in a truly distributed manner and pooling of neural activity within local circuits is much more effective than previously anticipated. Thus, the representation in early sensory areas does not appear to be impaired substantially by shared sensory noise and limitations in behavioral performance in psychophysical tasks may need to be attributed to processes downstream of the sensory population.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://areadne.org/2014/home.html},
event_place = {Santorini, Greece},
event_name = {AREADNE 2014: Research in Encoding and Decoding of Neural Ensembles},
author = {Cotton, RJ and Froudarakis, E and Ecker, AS and Berens, P and Saggau, P and Tolias, AS}
}
@Poster { EckerBCSDCSBT2014_2,
title = {State Dependence of Noise Correlation in Macaque Primary Visual Cortex},
year = {2014},
month = {6},
pages = {64},
abstract = {Shared, trial-to-trial variability in neuronal populations has a strong impact on the accuracy of information processing in the brain. Estimates of the level of such noise correlations are diverse, ranging from 0.01 to 0.4, with little consensus on which factors account for these
differences. Here we addressed one important factor that varied across studies, asking how anesthesia affects the population activity structure in macaque primary visual cortex. We found that under opioid anesthesia, activity was dominated by strong coordinated fluctuations on a timescale of 1–2 Hz, which were mostly absent in awake, fixating monkeys. Accounting for these global fluctuations markedly reduced correlations under anesthesia, matching those
observed during wakefulness and reconciling earlier studies conducted under anesthesia and in awake animals. Our results show that internal signals, such as brain state transitions under anesthesia, can induce noise correlations, but can also be estimated and accounted for based on neuronal population activity.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://areadne.org/2014/home.html},
event_place = {Santorini, Greece},
event_name = {AREADNE 2014: Research in Encoding and Decoding of Neural Ensembles},
author = {Ecker, AS and Berens, P and Cotton, RJ and Subramaniyan, M and Denfield, GH and Cadwell, CR and Smirnakis, SM and Bethge, M and Tolias, AS}
}
@Poster { GatysETB2013,
title = {Information Coding in the Variance of Neural Activity},
year = {2013},
month = {9},
pages = {44},
abstract = {Neural activity in the cortex appears to be notoriously noisy. A widely accepted explanation for this finding is that excitatory and inhibitory inputs to downstream neurons are balanced in a way that the upstream population activity does not affect the mean but only the variance of the input current. This can be thought of as a multiplicative noise channel. However, the capacity limits imposed by this information channel are not known. Here we develop a general understanding of the encoding process in terms of scale mixture processes and derive information-theoretic bounds on their performance. Our results show that signal transmission via instantaneous changes in the variance can behave quite differently from the common additive noise channel. We perform systematic numerical analyses to maximize the information across the variance channel and thus obtain tight lower bounds to its capacity. Furthermore, we found that additional noise, resembling the unreliable synaptic transmission of spikes, can surprisingly enhance the coding performance of the channel.},
department = {Research Group Bethge},
department2 = {Department Sch{\"o}lkopf},
web_url = {https://portal.g-node.org/abstracts/bc13/\#/doi/nncn.bc2013.0020},
event_place = {T{\"u}bingen, Germany},
event_name = {Bernstein Conference 2013},
DOI = {10.12751/nncn.bc2013.0020},
author = {Gatys, L and Ecker, A and Tchumatchenko, T and Bethge, M}
}
@Poster { FroudarakisBCESBT2013,
title = {Encoding of natural scene statistics in the primary visual cortex of the mouse},
year = {2013},
month = {3},
number = {II-76},
department = {Research Group Bethge},
web_url = {http://www.cosyne.org/c/index.php?title=Cosyne_13},
event_place = {Salt Lake City, UT, USA},
event_name = {Computational and Systems Neuroscience Meeting (COSYNE 2013)},
author = {Froudarakis, E and Berens, P and Cotton, JR and Ecker, AS and Saggau, P and Bethge, M and Tolias, A}
}
@Poster { EckerBTB2012_2,
title = {The correlation structure induced by fluctuations in attention},
year = {2012},
month = {6},
pages = {56},
abstract = {How attention shapes the structure of population activity has attracted substantial interest over the past decades. Attention has traditionally been associated with an increase in firing rates, reflecting a change in the gain of the population. More recent studies also report a
change in noise correlations, which is thought to reflect changes in functional connectivity.
However, since the degree of attention can vary substantially from trial to trial even within one experimental condition, the measured correlations could actually reflect fluctuations in the attention-related feedback signal (gain) rather than feed-forward noise, as often assumed.
To gain insights into this issue we analytically analyzed the standard model of spatial attention, where directing attention to the receptive field of a neuron increases its response gain. We assumed conditionally independent neurons (no noise correlations) and asked how uncontrolled
fluctuations in attention affect the correlation structure.
First, we found that this simple model of spatial attention explains the empirically measured correlation structure quite well. In addition to a positive average level of correlations, it predicts both an increase in correlations with firing rates, as observed in many studies, and a
decrease in correlations with the difference of two neurons’ tuning functions — a structure generally referred to as limited range correlations.
Second, we asked how fluctuations in attention would affect the accuracy of a population code, if treated as noise
by a downstream readout. Based on previous theoretical results, it would be expected that they negatively affect
readout accuracy because of the limited range correlations they induce. Surprisingly, we found that this is not
the case: correlations due to random gain fluctuations do not affect readout accuracy because their major axis is
orthogonal to changes in the stimulus orientation.
Our results can be readily generalized to include feature-based attention. The model has very few free parameters and can potentially account for a large fraction of the experimentally observed spike count (co-)variance.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
department3 = {Department Sch{\"o}lkopf},
web_url = {http://areadne.org/2012/home.html},
event_place = {Santorini, Greece},
event_name = {AREADNE 2012: Research in Encoding and Decoding of Neural Ensembles},
author = {Ecker, AS and Berens, P and Tolias, AS and Bethge, M}
}
@Poster { EckerBTB2012,
title = {The correlation structure induced by fluctuations in attention},
year = {2012},
month = {2},
volume = {9},
pages = {180},
abstract = {Attention has traditionally been associated with an increase in firing rates, reflecting a change in the gain of the
population. More recent studies also report a change in noise correlations, which is thought to reflect changes
in functional connectivity. However, since the degree of attention can vary substantially from trial to trial even
within one experimental condition, the measured correlations could actually reflect fluctuations in the attentionrelated feedback signal (gain) rather than feed-forward noise, as often assumed. To gain insights into this issue we analytically analyzed the standard model of spatial attention, where directing attention to the receptive field of a neuron increases its response gain. We assumed conditionally independent neurons (no noise correlations) and asked how uncontrolled fluctuations in attention affect the correlation structure. First, we found that this simple model of spatial attention explains the empirically measured correlation structure quite well. In addition to a positive average level of correlations, it predicts both an increase in correlations with firing rates, as observed in many studies, and a decrease in correlations with the difference of two neurons’ tuning functions—a structure generally referred to as limited range correlations. Second, we asked how fluctuations in attention would affect the accuracy of a population code, if treated as noise by a downstream readout. Based on previous theoretical results, it would be expected that they negatively affect readout accuracy because of the limited range correlations they induce. Surprisingly, we found that this is not the case: correlations due to random gain fluctuations do not affect readout accuracy because their major axis is orthogonal to changes in the stimulus orientation. Our results can be readily generalized to include feature-based attention. The model has very few free parameters and can potentially account for a large fraction of the observed spike count (co-)variance.},
department = {Research Group Bethge},
department2 = {Department Sch{\"o}lkopf},
web_url = {http://www.cosyne.org/c/index.php?title=Cosyne_12},
event_place = {Salt Lake City, UT, USA},
event_name = {9th Annual Computational and Systems Neuroscience Meeting (Cosyne 2012)},
author = {Ecker, A and Berens, P and Tolias, A and Bethge, M}
}
@Poster { BerensEGTB2011_2,
title = {Optimal Population Coding, Revisited},
year = {2011},
month = {2},
number = {III-67},
abstract = {Cortical circuits perform computations within few dozens of milliseconds with each neuron emitting only a few spikes. In this regime conclusions based on Fisher information, which is commonly used to assess the quality of population codes, are not always valid. Here we revisit the effect of tuning function width and correlation structure on neural population codes for angular variables using ideal observer analysis in both reconstruction and classification tasks employing Monte-Carlo simulations and analytical derivations. We show that the optimal tuning width of individual neurons and the optimal correlation structure of the population depend on the signal-to-noise ratio for both the reconstruction and the classification task. Strikingly, both ideal observers lead to very similar conclusions at low signal-to-noise ratio. In contrast, Fisher information favors severely suboptimal coding schemes in this regime. To further investigate the coding properties of Fisher-optimal codes, we compute the full neurometric functions of an ideal observer in the stimulus discrimination task, which allows us to evaluate population codes separately for fine and coarse discrimination. We find that codes with Fisher-optimal tuning width show strikingly bad performance for simple coarse discrimination tasks with a {\"e}pedestal error{\'i}, which is independent of population size. We show analytically that this is a necessary consequence of the fact that in such codes only few neurons are activated by each stimulus, irrespective of the population size. Further we show that the initial region of the neurometric function goes to zero with increasing population size. As a consequence, the overall error achieved by Fisher-optimal ensembles saturates for large populations. In summary, based on exact ideal observer analysis for both stimulus reconstruction and discrimination tasks we obtained (1) an accurate assessment of neural population codes at all signal-to-noise ratios and (2) analytical insights into the suboptimal behavior of Fisher-optimal population codes.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
department3 = {Department Sch{\"o}lkopf},
web_url = {http://www.cosyne.org/c/index.php?title=Cosyne_11_posters3},
event_place = {Salt Lake City, UT, USA},
event_name = {Computational and Systems Neuroscience Meeting (COSYNE 2011)},
author = {Berens, P and Ecker, AS and Gerwinn, S and Tolias, AS and Bethge, M}
}
@Poster { 7055,
title = {Decorrelated neuronal firing in cortical microcircuits},
year = {2010},
month = {11},
volume = {40},
number = {73.20},
abstract = {Correlated trial-to-trial variability in the activity of cortical neurons is thought to reflect the functional connectivity of the circuit. Many cortical areas are organized into functional columns, in which neurons are believed to be densely connected and share common input. Numerous studies report a high degree of correlated variability between nearby cells. We developed chronically implanted multi-tetrode arrays offering unprecedented recording quality to re-examine this question in primary visual cortex of awake macaques. We found that even nearby neurons with similar orientation tuning show virtually no correlated variability.
In a total of 46 recording sessions from two monkeys, we presented either static or drifting sine-wave gratings at eight different orientations. We recorded from 407 well isolated, visually responsive and orientation-tuned neurons, resulting in 1907 simultaneously recorded pairs of neurons. In 406 of these pairs both neurons were recorded by the same tetrode.
Despite being physically close to each other and having highly overlapping receptive fields, neurons recorded from the same tetrode had exceedingly low spike count correlations (rsc = 0.005 ± 0.004; mean ± SEM). Even cells with similar preferred orientations (rsignal > 0.5) had very weak correlations (rsc = 0.028 ± 0.010). This was also true if pairs were strongly driven by gratings with orientations close to the cells’ preferred orientations.
Correlations between neurons recorded by different tetrodes showed a similar pattern. They were low on average (rsc = 0.010 ± 0.002) with a weak relation between tuning similarity and spike count correlations (two-sample t test, rsignal < 0.5 versus rsignal > 0.5: P = 0.003, n = 1907).
To investigate whether low correlations also occur under more naturalistic stimulus conditions, we presented natural images to one of the monkeys. The average rsc was close to zero (rsc = 0.001 ± 0.005, n = 329) with no relation between receptive field overlap and spike count correlations. We obtained a similar result during stimulation with moving bars in a third monkey (rsc = 0.014 ± 0.011, n = 56).
Our findings suggest a refinement of current models of cortical microcircuit architecture and function: either adjacent neurons share only a few percent of their inputs or, alternatively, their activity is actively decorrelated.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://www.sfn.org/am2010/index.aspx?pagename=abstracts_main},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {San Diego, CA, USA},
event_name = {40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010)},
language = {en},
author = {Ecker, AS and Berens, P and Keliris, GA and Bethge, M and Logothetis, NK and Tolias, AS}
}
@Poster { 6810,
title = {Decorrelated Firing in Cortical Microcircuits},
year = {2010},
month = {6},
volume = {2010},
pages = {58},
abstract = {Correlated trial-to-trial variability in the activity of cortical neurons is thought to reflect the
functional connectivity of the circuit. Many cortical areas are organized into functional columns,
in which neurons are believed to be densely connected and share common input. Numerous
studies report a high degree of correlated variability between nearby cells. We developed
chronically implanted multi-tetrode arrays offering unprecedented recording quality
to re-examine this question in primary visual cortex of awake macaques. We found that
even nearby neurons with similar orientation tuning show virtually no correlated variability.
In a total of 46 recording sessions from two monkeys, we presented either static or drifting
sine-wave gratings at eight different orientations. We recorded from 407 well isolated, visually
responsive and orientation-tuned neurons, resulting in 1907 simultaneously recorded
pairs of neurons. In 406 of these pairs both neurons were recorded by the same tetrode.
Despite being physically close to each other and having highly overlapping receptive fields,
neurons recorded from the same tetrode had exceedingly low spike count correlations (rsc =
0.005 ± 0.004; mean ± SEM). Even cells with similar preferred orientations (rsignal > 0.5) had
very weak correlations (rsc = 0.028 ± 0.010). This was also true if pairs were strongly driven
by gratings with orientations close to the cells’ preferred orientations.
Correlations between neurons recorded by different tetrodes showed a similar pattern. They
were low on average (rsc = 0.010 ± 0.002) with a weak relation between tuning similarity
and spike count correlations (two-sample t test, rsignal < 0.5 versus rsignal > 0.5: P = 0.003, n =
1907).
To investigate whether low correlations also occur under more naturalistic stimulus conditions,
we presented natural images to one of the monkeys. The average rsc was close to zero
(rsc = 0.001 ± 0.005, n = 329) with no relation between receptive field overlap and spike
count correlations. We obtained a similar result during stimulation with moving bars in a
third monkey (rsc = 0.014 ± 0.011, n = 56).
Our findings suggest a refinement of current models of cortical microcircuit architecture and
function: either adjacent neurons share only a few percent of their inputs or, alternatively,
their activity is actively decorrelated.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
web_url = {http://www.areadne.org/2010/home.html},
editor = {Hatsopoulos, N. G., S. Pezaris},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Santorini, Greece},
event_name = {AREADNE 2010: Research in Encoding And Decoding of Neural Ensembles},
language = {en},
author = {Ecker, AS and Berens, P and Keliris, GA and Bethge, M and Logothetis, NK and Tolias, AS}
}
@Poster { 5844,
title = {Sensory input statistics and network mechanisms in primate primary visual cortex},
journal = {Frontiers in Systems Neuroscience},
year = {2009},
month = {3},
volume = {2009},
number = {Conference Abstracts: Computational and Systems Neuroscience},
abstract = {Understanding the structure of multi-neuronal firing patterns in ensembles of cortical neurons is a major challenge for systems neuroscience. The dependence of network properties on the statistics of the sensory input can provide important insights into the computations performed by neural ensembles. Here, we study the functional properties of neural populations in the primary visual cortex of awake, behaving macaques by varying visual input statistics in a controlled way. Using arrays of chronically implanted tetrodes, we record simultaneously from up to thirty well-isolated neurons while presenting sets of images with three different correlation structures: spatially uncorrelated white noise (whn), images matching the second-order correlations of natural images (phs) and natural images including higher-order correlations (nat).
We find that groups of six nearby cortical neurons show little redundancy in their firing patterns (represented as binary vectors, 10ms bins) but rather act almost independently (mean multi-information 0.85 bits/s, range 0.16 - 1.90 bits/s, mean fraction of marginal entropy 0.34 \%, N=46). Although network correlations are weak, they are statistically significant. While relatively few groups showed significant redundancies under stimulation with white noise (67.4 ± 3.2\%; mean fraction of groups ± S.E.M.), many more did so in the other two conditions (phs: 95.7 ± 0.6\%; nat: 89.1 ± 1.4\%). Additional higher-order correlations in natural images compared to phase scrambled images did not increase but rather decrease the redundancy in the cortical representation: Network correlations are significantly higher in phs than in nat, as is the number of significantly correlated groups.
Multi-information measures the reduction in entropy due to any form of correlation. By using second order maximum entropy modeling, we find that a large fraction of multi-information is accounted for by pairwise correlations (whn: 75.0 ± 3.3\%; phs: 82.8 ± 2.1\%; nat: 80.8 ± 2.4\%; groups with significant redundancy). Importantly, stimulation with natural images containing higher-order correlations only lead to a slight increase in the fraction of redundancy due to higher-order correlations in the cortical representation (mean difference 2.26 \%, p=0.054, Sign test).
While our results suggest that population activity in V1 may be modeled well using pairwise correlations only, they leave roughly 20-25 \% of the multi-information unexplained. Therefore, choosing a particular form of higher-order interactions may improve model quality. Thus, in addition to the independent model, we evaluated the quality of three different models: (a) The second-order maximum entropy model, which minimizes higher-order correlations, (b) a model which assumes that correlations are a product of common inputs (Dichotomized Gaussian) and (c) a mixture model in which correlations are induced by a discrete number of latent states. We find that an independent model is sufficient for the white noise condition but neither for phs or nat. In contrast, all of the correlation models (a-c) perform similarly well for the conditions with correlated stimuli.
Our results suggest that under natural stimulation redundancies in cortical neurons are relatively weak. Higher-order correlations in natural images do not increase but rather decrease the redundancies in the cortical representation.},
department = {Research Group Bethge},
web_url = {http://www.cosyne.org/c/index.php?title=Cosyne_09},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Salt Lake City, UT, USA},
event_name = {Computational and Systems Neuroscience Meeting (COSYNE 2009)},
language = {en},
DOI = {10.3389/conf.neuro.06.2009.03.298},
author = {Berens, P and Macke, JH and Ecker, AS and Cotton, RJ and Bethge, M and Tolias, AS}
}
@Poster { 5359,
title = {Towards the neural basis of the flash-lag effect},
journal = {International Workshop on Aspects of Adaptive Cortex Dynamics},
year = {2008},
month = {9},
volume = {2008},
pages = {1},
department = {Department Sch{\"o}lkopf},
department2 = {Research Group Bethge},
web_url = {http://www.ikw.uni-osnabrueck.de/nbp/PDFs_Publications/Delmenhorst_Programm_040908.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
author = {Ecker, AS and Berens, P and Hoenselaar, A and Subramaniyan, M and Tolias, AS and Bethge, M}
}
@Poster { MackeBEOTB2008,
title = {Modeling populations of spiking neurons with the Dichotomized Gaussian distribution},
year = {2008},
month = {7},
department = {Research Group Bethge},
department2 = {Department Logothetis},
web_url = {http://www.theswartzfoundation.org/summer-meeting-2008.asp},
event_place = {Princeton, NJ, USA},
event_name = {Annual Meeting 2008 of Sloan-Swartz Centers for Theoretical Neurobiology},
author = {Macke, JH and Berens, P and Ecker, AS and Opper, M and Tolias, AS and Bethge, M}
}
@Poster { 5101,
title = {Flexible Models for Population Spike Trains},
year = {2008},
month = {6},
pages = {48},
abstract = {In order to understand how neural systems perform computations and process sensory
information, we need to understand the structure of firing patterns in large populations of
neurons. Spike trains recorded from populations of neurons can exhibit substantial pair wise
correlations between neurons and rich temporal structure. Thus, efficient methods for
generating artificial spike trains with specified correlation structure are essential for the
realistic simulation and analysis of neural systems.
Here we show how correlated binary spike trains can be modeled by means of a latent
multivariate Gaussian model. Sampling from our model is computationally very efficient, and
in particular, feasible even for large populations of neurons. We show empirically that the
spike trains generated with this method have entropy close to the theoretical maximum. They
are therefore consistent with specified pair-wise correlations without exhibiting systematic
higher-order correlations. We compare our model to alternative approaches and discuss its
limitations and advantages. In addition, we demonstrate its use for modeling temporal
correlations in a neuron recorded in macaque primary visual cortex.
Neural activity is often summarized by discarding the exact timing of spikes, and only
counting the total number of spikes that a neuron (or population) fires in a given time window.
In modeling studies, these spike counts have often been assumed to be Poisson distributed
and neurons to be independent. However, correlations between spike counts have been
reported in various visual areas. We show how both temporal and inter-neuron correlations
shape the structure of spike counts, and how our model can be used to generate spike counts
with arbitrary marginal distributions and correlation structure. We demonstrate its capabilities
by modeling a population of simultaneously recorded neurons from the primary visual cortex
of a macaque, and we show how a model with correlations accounts for the data far better
than a model that assumes independence.},
department = {Department Sch{\"o}lkopf},
department2 = {Research Group Bethge},
web_url = {http://www.areadne.org/2008/home.html},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Santorini, Greece},
event_name = {AREADNE 2008: Research in Encoding and Decoding of Neural Ensembles},
language = {en},
author = {Bethge, M and Macke, JH and Berens, P and Ecker, AS and Tolias, AS}
}
@Poster { 5100,
title = {Pairwise Correlations and Multineuronal Firing Patterns in the Primary Visual Cortex of the Awake, Behaving Macaque},
year = {2008},
month = {6},
pages = {46},
abstract = {Understanding the structure of multi-neuronal firing patterns has been a central quest and
major challenge for systems neuroscience. In particular, how do pairwise interactions between
neurons shape the firing patterns of neuronal ensembles in the cortex? To study this
question, we recorded simultaneously from multiple single neurons in the primary visual
cortex of an awake, behaving macaque using an array of chronically implanted tetrodes1. High
contrast flashed and moving bars were used for stimulation, while the monkey was required to
maintain fixation.
In a similar vein to recent studies of in vitro preparations2,3,5, we applied maximum entropy
analysis for the first time to the binary spiking patterns of populations of cortical neurons
recorded in vivo from the awake macaque. We employed the Dichotomized Gaussian
distribution, which can be seen as a close approximation to the pairwise maximum-entropy
model for binary data4. Surprisingly, we find that even pairs of neurons with nearby receptive
fields (receptive field center distance < 0.15\(^{\circ}\)) have only weak correlations between their
binary responses computed in bins of 10 ms (median absolute correlation coefficient: 0.014,
0.010-0.019, 95\% confidence intervals, N=95 pairs; positive correlations: 0.015, N=59;
negative correlations: -0.013, N=36). Accordingly, the distribution of spiking patterns of
groups of 10 neurons is described well with a model that assumes independence between
individual neurons (Jensen-Shannon-Divergence: 1.06\(\times\)10-2 independent model, 0.96\(\times\)10-2
approximate second-order maximum-entropy model4; H/H1=0.992). These results suggest that
the distribution of firing patterns of small cortical networks in the awake animal is
predominantly determined by the mean activity of the participating cells, not by their
interactions.
Meaningful computations, however, are performed by neuronal populations much larger than
10 neurons. Therefore, we investigated how weak pairwise correlations affect the firing
patterns of artificial populations4 of up to 1000 cells with the same correlation structure as
experimentally measured. We find that in neuronal ensembles of this size firing patterns with
many active or silent neurons occur considerably more often than expected from a fully
independent population (e.g. 130 or more out of 1000 neurons are active simultaneously
roughly every 300 ms in the correlated model and only once every 3-4 seconds in the
independent model). These results suggest that the firing patterns of cortical networks
comparable in size to several minicolumns exhibit a rich structure, even if most pairs appear
relatively independent when studying small subgroups thereof.},
department = {Department Sch{\"o}lkopf},
department2 = {Research Group Bethge},
web_url = {http://www.areadne.org/2008/home.html},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Santorini, Greece},
event_name = {AREADNE 2008: Research in Encoding and Decoding of Neural Ensembles},
language = {en},
author = {Berens, P and Ecker, AS and Subramaniyan, M and Macke, JH and Hauck, P and Bethge, M and Tolias, AS}
}
@Poster { 4591,
title = {On the spatial scale of the local field potential - orientation and ocularity tuning of the local field potential in the primary visual cortex of the macaque},
year = {2007},
month = {11},
volume = {37},
number = {176.7},
abstract = {The local field potential (LFP) and, in particular, the gamma-band frequency range (30-90 Hz) have recently received much attention, as numerous studies have shown correlations between LFP and sensory, motor and cognitive variables in various cortical regions. However, the extent to which it reflects the activity of local populations of neurons remains elusive. The issue of spatial scale is central for understanding the origins of the LFP and how this signal can be used to study the functional organization of the brain.
We addressed this question by simultaneously recording multi-unit spiking activity (MUA) and LFP from the primary visual cortex (V1) of awake, behaving macaques using arrays of tetrodes. Oriented gratings were used for visual stimulation, applied either binocular or monocular. The columnar organization of stimulus orientation and ocularity in V1 provides an excellent opportunity to study the spatial precision of the LFP signal, because neurons with similar orientation preference are organized at the fine spatial scale of cortical microcolumns (50-100 \(\mu\)m), whereas ocular dominance columns span around 450 \(\mu\)m.
As shown before, we find that the increase of LFP gamma-band power is a function of orientation and ocularity of the stimulus. However, the power of the gamma-band contains much less information about the orientation of the stimulus than the MUA recorded at the same site. The average discriminability d' between preferred and orthogonal orientation was 2.46±0.15 for MUA and 1.01±0.05 for LFP (mean ±std). Moreover, we find only a weak correlation between the preferred orientation of the MUA tuning function and that of the LFP (r=0.21, p<0.05). In contrast, we find a strong correlation between the preferred ocularity of the two signals (r=0.53, p<1e-9).
We therefore conclude that the gamma-power of the LFP does not reflect well the local activity on the scale of orientation columns but does capture the ocular dominance structure of V1. We suggest that gamma-band activity is generated by ensembles of neurons larger than 50-100 \(\mu\)m. In agreement with a previous study (Liu \& Newsome, 2006) we find that it more likely resembles the activity of neurons from an area spanning a few hundred micrometers.},
department = {Department Logothetis},
web_url = {http://www.sfn.org/am2007/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {San Diego, CA, USA},
event_name = {37th Annual Meeting of the Society for Neuroscience (Neuroscience 2007)},
language = {en},
author = {Berens, P and Ecker, AS and Keliris, GA and Logothetis, NK and Tolias, AS}
}
@Poster { 4733,
title = {Recording chronically from the same neurons in awake, behaving primates},
year = {2007},
month = {11},
volume = {37},
number = {176.8},
abstract = {Understanding the mechanisms of learning and memory consolidation requires characterizing how the response properties of individual neurons and interactions across populations of neurons change over time, during periods spanning multiple days.
We used multiple chronically implanted tetrodes to record single unit activity from area V1 of the awake, behaving macaque and developed a method to quantitatively determine recording stability. Our method is based on a statistical framework which uses similarity of action potential waveforms to detect stable recordings given a pre-defined type I error rate. The similarity measure that was used takes into account both the shape of the action potential waveform and the amplitude ratio across channels, which depends on the location of the neuron relative to the tetrode.
271 well-isolated single units were recorded from 7 tetrodes during two periods of up to 23 days. We computed the distribution of pairwise similarities of average waveforms recorded on consecutive recording sessions during the first 34 days after implantation of the chronic drive. During this period, there was no recording stability due to regular adjustments of the tetrodes. We used this distribution as an empirical null distribution for hypothesis testing.
Using this statistical procedure and a type I error rate of alpha = 0.05, we find that of all single units recorded on a given day, 51\% could be recorded for at least 2 days, 40\% for at least 3 days, and 25\% for at least 7 days.
In addition, we adapted a recently proposed multivariate statistical test (Gretton et al., 2007) to test whether the waveforms obtained at consecutive days come from the same underlying probability distribution. Using this test we obtained qualitatively similar results.
To validate these results, we compared orientation tuning functions of neurons that were tracked across days. Consistent with the claim that the same neurons were recorded across days and the fact that the monkey was not performing a learning task, the distribution of tuning differences of stable and orientation-tuned neurons across days was highly significantly different (Wilcoxon rank sum test, n1 = 79, n2 = 582, p < 10\verb=^=-34) from the distribution of tuning differences across different neurons.
Our results show that using only waveform information it is possible to reliably track stable neurons across days with a limited type I error probability. This statistical approach is particularly important since, in a learning experiment, properties of neurons such as orientation tuning are potentially changed and therefore cannot be used to evaluate stability.},
department = {Department Logothetis},
web_url = {http://www.sfn.org/am2007/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {San Diego, CA, USA},
event_name = {37th Annual Meeting of the Society for Neuroscience (Neuroscience 2007)},
language = {en},
author = {Ecker, AS and Siapas, AG and Hoenselaar, A and Berens, P and Keliris, GA and Logothetis, NK and Tolias, AS}
}
@Poster { 4731,
title = {Studying the effects of noise correlations on population coding using a sampling method},
year = {2007},
month = {9},
volume = {2007},
pages = {21-22},
abstract = {Responses of single neurons to a fixed stimulus are usually both variable and highly ambiguous. Therefore,
it is widely assumed that stimulus parameters are encoded by populations of neurons. An important
aspect in population coding that has received much interest in the past is the effect of correlated noise
on the accuracy of the neural code.
Theoretical studies have investigated the effects of different correlation structures on the amount of
information that can be encoded by a population of neurons based on Fisher Information. Unfortunately,
to be analytically tractable, these studies usually have to make certain simplifying assumptions such as
high firing rates and Gaussian noise. Therefore, it remains open if these results also hold in the more realistic scenario of low firing rates and discrete, Poisson-distributed spike counts.
In order to address this question we have developed a straightforward and efficient method to draw samples
from a multivariate near-maximum entropy Poisson distribution with arbitrary mean and covariance
matrix based on the dichotomized Gaussian distribution [1]. The ability to extensively sample data from
this class of distributions enables us to study the effects of different types of correlation structures and
tuning functions on the information encoded by populations of neurons under more realistic assumptions
than analytically tractable methods.
Specifically, we studied how limited range correlations (neurons with similar tuning functions and low
spatial distance are more correlated than others) affect the accuracy of a downstream decoder compared
to uniform correlations (correlations between neurons are independent of their properties and locations).
Using a set of neurons with equally spaced orientation tuning functions, we computed the error of an
optimal linear estimator (OLE) reconstructing stimulus orientation from the neurons firing rates. We
findsupporting previous theoretical resultsthat irrespective of tuning width and the number of neurons in
the network, limited range correlations decrease decoding accuracy while uniform correlations facilitate
accurate decoding. The optimal tuning width, however, did not change as a function of either the
correlation structure or the number of neurons in the network. These results are particularly interesting
since a number of experimental studies report limited range correlation structures (starting at around
0.1 to 0.2 for similar neurons) while experiments carried out in our own lab suggest that correlations are
generally low (on the order of 0.01) and uniform.},
department = {Department Sch{\"o}lkopf},
department2 = {Department Logothetis},
department3 = {Research Group Bethge},
web_url = {http://www.gatsby.ucl.ac.uk/nccd/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Hossegor, France},
event_name = {Neural Coding, Computation and Dynamics (NCCD 07)},
language = {en},
author = {Ecker, AS and Berens, P and Bethge, M and Logothetis, NK and Tolias, AS}
}
@Poster { 4272,
title = {A Data Management System for Electrophysiological Data Analysis},
journal = {Neuroforum},
year = {2007},
month = {4},
volume = {13},
number = {Supplement},
pages = {1222},
abstract = {Recent advances in both electrophysiological recording techniques and hardware capabilities have enabled
researchers to simultaneously record from a large number of neurons in different areas of the brain. This opens
the door for a wide range of complex analyses potentially leading to a better understanding of the principles
underlying neural network computations. At the same time, due to the increasing amount of data with
increasing complexity, significantly more emphasis has to be put on the data analysis task. Although
high-level scripting languages such as Matlab can speed up the development of analysis tools, in our
experience, a too large amount of time is still spent on (re)structuring and (re)organizing data for specific
analyses.
Therefore, our goal was to develop a system which enables experimental neuroscientists to spend less time on
organizing their data and more on data collection and creative analysis. We developed an object oriented
Matlab toolbox which supplies the user with basic data types and functions to organize and structure various
types of electrophysiological data. By using an object oriented, hierarchical layout, basic functionality, such as
integration of metadata, or storage and retrieval of data and results, is implemented independent of specific
data formats or experimental designs. This provides maximal flexibility and compatibility with future
experiments and new data formats. All data and experimental results are stored in a database, so the
experimenter can choose which data to keep in memory for faster access and which to save to disk to save
resources. Additionally, we have created an extensive library of basic analysis and visualization tools that can
be used to get an overview of the data.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/EckerTolias_2007_ADataManagement_4272[0].pdf},
department = {Department Logothetis},
web_url = {http://www.neuro.uni-goettingen.de/nbc.php?sel=archiv},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {7th Meeting of the German Neuroscience Society, 31st G{\"o}ttingen Neurobiology Conference},
language = {en},
author = {Ecker, AS and Berens, P and Keliris, GA and Logothetis, NK and Tolias, AS}
}
@Poster { 4273,
title = {Orientation tuning of the local field potential and multi-unit activity in the primary visual cortex of the macaque},
journal = {Neuroforum},
year = {2007},
month = {4},
volume = {13},
number = {Supplement},
pages = {735},
abstract = {Oscillations in the local field potential (LFP) are abundant across species and brain regions. The possible
relationship of these low-frequency extracelluar voltage fluctuations with the activity of the underlying local
population of neurons remains largely elusive. To study this relationship, we used an array of chronically
implanted tetrodes spanning a distance of 700 \&\#956;m and simultaneously recorded action potentials from multiple
well-isolated single units, multi unit activity (MUA) and LFP from area V1 of the awake, behaving macaque.
Moving and static gratings of different orientations were used for visual stimulation.
In agreement with previous studies we find that the increase of LFP gamma-band power is a function of the
orientation of the stimulus. However, the power of the gamma-band contains much less information about the
orientation of the stimulus than the MUA and SUA recorded at the same site (Figure 1A). The average
discriminability d‘ between preferred and orthogonal orientation was 2.46 for MUA, 2.45 for SUA and 1.01
for the LFP. Moreover, in contrast to recent results from area MT (Liu and Newsome, 2006) we find only a
weak correlation between the preferred orientation of the MUA tuning function and that of the LFP (Figure
1B, different colors indicate different animals). Interestingly, all nearby LFP recording sites in our array were
tuned to a similar orientation while the preferred orientations of MUA tuning functions were widely scattered.
These results suggest that the power of LFP signals does not capture local population activity at the scale of
orientation columns in area V1.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/T16-4C_[0].pdf},
department = {Department Logothetis},
web_url = {http://www.neuro.uni-goettingen.de/nbc.php?sel=archiv},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {7th Meeting of the German Neuroscience Society, 31st G{\"o}ttingen Neurobiology Conference},
language = {en},
author = {Berens, P and Keliris, GA and Ecker, AS and Logothetis, NK and Tolias, AS}
}
@Poster { 3949,
title = {Spikes are phase locked to the gamma-band of the local field potential oscillations in the primary visual cortex of the macaque},
year = {2006},
month = {6},
pages = {39},
abstract = {Oscillations in the local field potential (LFP) are abundant across species and brain regions. The possible
role of these oscillations in information processing in the primary visual cortex (V1) of the macaque still
remains largely elusive despite that V1 is one of the most extensively studied brain areas. To this end, we
used chronically implanted, multiple tetrodes and recorded the spiking activity of single neurons and LFPs
from area V1 of the awake, behaving macaque. Moving and static gratings of different orientations were
used for visual stimulation.
In agreement with previous reports we find that the increase of the LFP gamma-band power is a function
of the orientation of the stimulus. Surprisingly though, there is only a weak correlation between the peak
of the multi-unit spiking activity orientation tuning functions and the peak of the orientation tuning function
of the gamma-band power of the LFP. There is however a different kind of relationship between spikes
and LFP. Namely, the timing of the spikes is not randomly distributed in time but instead is locked to the
phase of the gamma-band of the LFP. Specifically, the spikes of 60 out of 151 well-isolated single units
showed significant phase locking to the LFP (P<0.05, circular Rayleigh test). On average, the spikes occurred
on the downward slope of the LFP oscillation. In contrast to the presence of phase precession reported
in the rat hippocampus, the phase tuning in V1 is stable over time. Specifically, the preferred
phase of the spikes does not seem to change over time during the presentation of the stimulus. Moreover,
the preferred phase is not significantly modulated as a function of the orientation of the stimulus (Figure
A).
This temporal structuring of the spiking activity of neurons in V1 could allow coding of information in the
temporal regime (Panzeri \& Schultz, 2001). In addition it could also potentially synchronize populations of
neurons (Fries 2005). We are currently investigating these conjectures.},
department = {Department Logothetis},
web_url = {http://www.areadne.org/2006/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Santorini, Greece},
event_name = {AREADNE 2006: Research in Encoding and Decoding of Neural Ensembles},
language = {en},
author = {Berens, P and Ecker, AS and Hoenselaar, A and Keliris, GA and Siapas, AG and Logothetis, NK and Tolias, AS}
}
@Poster { ToliasEKSSL2006,
title = {Structure of interneuronal correlations in the primary visual cortex of the rhesus macaque},
year = {2006},
month = {3},
pages = {13},
abstract = {Despite recent progress in systems neuroscience, basic properties of the neural code still remain obscure. For instance, the responses of single neurons are both highly variable and ambiguous (similar responses can be elicited by different types of stimuli). This variability/ambiguity has to be resolved by considering the joint pattern of firing of multiple single units responding simultaneously to a stimulus. Therefore, in order to understand the underlying principles of the neural code it is important to characterize the correlations between neurons and the impact that these correlations have on the amount of information that can be encoded by populations of neurons. Here we applied the technique of chronically implanted, multiple tetrodes to record simultaneously from a number of neurons in the primary visual cortex (V1) of the awake behaving macaque, and to measure the correlations in the trial-to-trial fluctuations of their firing rates under the same stimulation conditions (noise correlations). We find that, contrary to widespread belief, noise correlations in V1 are very small (around 0.01) and do not change systematically neither as a function of cortical distance (up to 600 um) nor as a function of the similarity in stimulus preference between the neurons (uniform correlation structure). Interestingly, a uniform correlation structure is predicted by theory to increase the achievable encoding accuracy of a neuronal population and may reflect a universal principle for population coding throughout the cortex.},
department = {Department Logothetis},
web_url = {http://www.cosyne.org/c/index.php?title=Cosyne_06},
event_place = {Salt Lake City, UT, USA},
event_name = {Computational and Systems Neuroscience Meeting (COSYNE 2006)},
author = {Tolias, AS and Ecker, A and Keliris, GA and Siapas, TG and Smirnakis, SM and Logothetis, NK}
}
@Thesis { 5104,
title = {Predictive Coding and Spike Timing Dependent Plasticity in Primary Visual Cortex},
year = {2008},
month = {3},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/diplthesis_ae_final_[0].pdf},
department = {Research Group Bethge},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Universit{\"a}t T{\"u}bingen, T{\"u}bingen, Germany},
type = {Diplom},
language = {en},
author = {Ecker, AS}
}
@Conference { GatysETB2015,
title = {Synaptic unreliability facilitates information transmission in balanced cortical populations},
year = {2015},
month = {3},
day = {16},
abstract = {Synaptic unreliability is one of the major sources of biophysical noise in the brain. In the context of neural information processing, it is a central question how neural systems can afford this unreliability. Here we examined how synaptic noise affects signal transmission in cortical circuits, where excitation and inhibition are thought to be tightly balanced. Surprisingly, we found that in this balanced state synaptic response variability actually facilitates information transmission, rather than impairing it. In particular, the transmission of fast-varying signals benefits from synaptic noise, as it instantaneously increases the amount of information shared between presynaptic signal and postsynaptic current. This finding provides a parsimonious explanation why cortex can afford to operate with noisy synapses.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
talk_type = {Abstract Talk},
web_url = {http://www.dpg-verhandlungen.de/year/2015/conference/berlin/part/bp/session/8/contribution/5},
event_place = {Berlin, Germany},
event_name = {79. Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG-Fr{\"u}hjahrstagung},
author = {Gatys, LA and Ecker, AS and Tchumatchenko, T and Bethge, M}
}
@Conference { GatysETB2014_2,
title = {Synaptic unreliability facilitates information transmission in balanced cortical populations},
year = {2014},
month = {10},
day = {13},
volume = {15},
pages = {11},
abstract = {Cortical neurons fire in a highly irregular manner, suggesting that their input is tightly balanced and changes in presynaptic firing rate are encoded primarily in the variance of the postsynaptic currents. Here we show that such balance has a surprising effect on information
transmission: Synaptic unreliability which is ubiquitous in cortex and usually thought to impair neural communication actually increases the information rate. We show that the
beneficial effect of noise is based on a very general mechanism which contrary to stochastic resonance does not rely on a threshold nonlinearity.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
talk_type = {Abstract Talk},
web_url = {http://www.neuroschool-tuebingen-nena.de/fileadmin/user_upload/Dokumente/neuroscience/Abstractbook_NeNa2014_final.pdf},
event_place = {Schramberg, Germany},
event_name = {15th Conference of Junior Neuroscientists of T{\"u}bingen (NeNa 2014)},
author = {Gatys, L and Ecker, A and Tchumatchenko, T and Bethge, M}
}
@Conference { GatysETB2014,
title = {Synaptic unreliability facilitates information transmission in
balanced cortical populations},
year = {2014},
month = {9},
day = {4},
pages = {21},
abstract = {Cortical neurons fire in a highly irregular manner, suggesting that their input is tightly balanced and changes in presynaptic firing rate are encoded primarily in the variance of the postsynaptic currents. Here we show that such balance has a surprising effect on information transmission: Synaptic unreliability – which is ubiquitous in cortex and usually thought to impair neural communication – actually increases the information rate. We show that the beneficial effect of noise is based on a very general mechanism which contrary to stochastic resonance does not rely on a threshold nonlinearity.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
talk_type = {Abstract Talk},
web_url = {http://abstracts.g-node.org/abstracts/65d2bbbf-5b2d-4570-8200-f994f190e9ca},
event_place = {G{\"o}ttingen, Germany},
event_name = {Bernstein Conference 2014},
DOI = {10.12751/nncn.bc2014.0017},
author = {Gatys, LA and Ecker, AS and Tchumatchenko, T and Bethge, M}
}
@Conference { Ecker2013,
title = {State dependence of noise correlations in macaque primary visual cortex},
year = {2013},
month = {7},
day = {18},
abstract = {The structure and magnitude of noise correlations in the monkey visual system has been subject to intense debate over the last couple of years. We previously found that neural responses to repeated presentations of the same visual stimulus were close to independent in V1 of awake, fixating monkeys (average rsc: 0.01). Other labs, in contrast, found average levels of correlations up to an order of magnitude higher. Although a number of possible explanations for this discrepancy have been put forward, only few of them have been directly addressed. We tested one of our original hypotheses, that fluctuations of global brain state under anesthesia may induce positive correlations between neurons, which are absent during wakefulness. We performed multi-tetrode recordings in V1 of opiod-anesthetized monkeys under conditions otherwise identical to our previous awake recordings. Activity in anesthetized monkey V1 was dominated by strong coordinated fluctuations involving nearly every active neuron. These state fluctuations evolve on a timescale of 1–2 Hz, substantially slower than what would be expected from shared sensory noise, and resemble up and down states, which have been described for many other types of anesthetics before. During wakefulness, in contrast, such state fluctuations were absent. We further found that after accounting for the brain state under anesthesia the level of noise correlations was reduced to that during wakefulness. Our results highlight an important caveat of neural population recordings under anesthesia: if not properly accounted for, state fluctuations, which are not present in awake animals, are the primary source of correlated variability.},
department = {Department Logothetis},
talk_type = {Invited Lecture},
web_url = {http://www.gnt.ens.fr/\verb=~=sostojic/cns2013_workshop.html},
event_place = {Paris, France},
event_name = {CNS 2013 Workshop on Functional Role of Correlations: Theory and Experiment},
author = {Ecker, A}
}
@Conference { BerensGEB2009,
title = {Neurometric function analysis of short-term population codes},
journal = {Frontiers in Computational Neuroscience},
year = {2009},
month = {10},
day = {1},
volume = {2009},
number = {Conference Abstract: Bernstein Conference on Computational Neuroscience},
pages = {24-25},
abstract = {The relative merits of different population coding schemes have mostly been studied in the framework of stimulus reconstruction using Fisher Information, minimum mean square error or mutual information. Here, we analyze neural population codes using the minimal discrimination error (MDE) and the Jensen-Shannon information in a two alternatives forced choice (2AFC) task. In a certain sense, this approach is more informative than the previous ones as it defines an error that is specific to any pair of possible stimuli - in particular, it includes Fisher Information as a special case. We demonstrate several advantages of the minimal discrimination error: (1) it is very intuitive and easier to compare to experimental data, (2) it is easier to compute than mutual information or minimum mean square error, (3) it allows studying assumption about prior distributions, and (4) it provides a more reliable assessment of coding accuracy than Fisher information.
First, we introduce the Jensen-Shannon information and explain how it can be used to bound the MDE. In particular, we derive a new lower bound on the minimal discrimination error that is tighter than previous ones. Also, we explain how Fisher information can be derived from the Jensen-Shannon information and conversely to what extent Fisher information can be used to predict the minimal discrimination error for arbitrary pairs of stimuli depending on the properties of the tuning functions.
Second, we use the minimal discrimination error to study population codes of angular variables. In particular, we assess the impact of different noise correlations structures on coding accuracy in long versus short decoding time windows. That is, for long time window we use the common Gaussian noise approximation while we analyze the Ising model with identical noise correlation structure to address the case of short time windows. As an important result, we find that the beneficial effect of stimulus dependent correlations in the absence of 'limited-range' correlations holds only true for long-term population codes while they provide no advantage in case of short decoding time windows.
In this way, we provide for a new rigorous framework for assessing the functional consequences of correlation structures for the representational accuracy of neural population codes in short time scales.},
department = {Research Group Bethge},
department2 = {Department Logothetis},
department3 = {Department Sch{\"o}lkopf},
talk_type = {Abstract Talk},
web_url = {http://www.frontiersin.org/10.3389/conf.neuro.10.2009.14.093/event_abstract},
event_place = {Frankfurt a.M., Germany},
event_name = {Bernstein Conference on Computational Neuroscience (BCCN 2009)},
DOI = {10.3389/conf.neuro.10.2009.14.093},
author = {Berens, P and Gerwinn, S and Ecker, AS and Bethge, M}
}
@Conference { ToliasEKPPL2007,
title = {Population codes, correlations and coding uncertainty},
year = {2007},
month = {9},
volume = {2007},
pages = {16},
abstract = {Despite progress in systems neuroscience the neural code still remains elusive. For instance, the responses
of single neurons are both highly variable and ambiguous (similar responses can be elicited by different
types of stimuli). This variability/ambiguity has to be resolved by considering the joint pattern of firing
of multiple single units responding simultaneously to a stimulus. Therefore, in order to understand the
underlying principles of the neural code it is imperative to characterize the correlations between neurons
and the impact that these correlations have on the amount of information encoded by populations of
neurons. We use chronically implanted tetrode arrays to record simultaneously from many neurons in
the primary visual cortex (V1) of awake, behaving macaques. We find that the correlations in the trialto-
trial fluctuations of their firing rates between neurons under the same stimulation conditions (noise
correlations) in V1 were very small (around 0.01 in 500 ms bin window) during passive viewing of sinusoidal
grating stimuli. We are also measuring correlations in extrastriate visual areas and investigating
the impact of correlations on encoding stimulus uncertainty by neuronal populations, under different
stimulus and behavioral conditions.},
department = {Department Logothetis},
department2 = {Research Group Bethge},
talk_type = {Abstract Talk},
web_url = {http://www.gatsby.ucl.ac.uk/nccd/abstracts/tolias.html},
event_place = {Hossegor, France},
event_name = {Neural Coding, Computation and Dynamics (NCCD 07)},
author = {Tolias, AS and Ecker, A and Keliris, GA and Panagiotaropolulos, F and Panzeri, S and Logothetis, NK}
}
@Conference { 3723,
title = {Structure of interneuronal correlations in the primary visual cortex of the Rhesus macaque},
year = {2005},
month = {11},
volume = {35},
number = {591.12},
abstract = {Despite recent progress in systems neuroscience, basic properties of the neural code still remain obscure. For instance, the responses of single neurons are both highly variable and ambiguous (similar responses can be elicited by different types of stimuli). This variability/ambiguity has to be resolved by considering the joint pattern of firing of multiple single units responding simultaneously to a stimulus. Therefore, in order to understand the underlying principles of the neural code it is important to characterize the correlations between neurons and the impact that these correlations have on the amount of information that can be encoded by populations of neurons. Here we applied the technique of chronically implanted, multiple tetrodes to record simultaneously from a number of neurons in the primary visual cortex (V1) of the awake behaving macaque, and to measure the correlations in the trial-to-trial fluctuations of their firing rates under the same stimulation conditions (noise correlations). We find
that, contrary to widespread belief, noise correlations in V1 are very small (around 0.01) and do not change systematically neither as a function of cortical distance (up to 600 m) nor as a function of the similarity in stimulus preference between the neurons (uniform correlation structure). Interestingly, a uniform correlation structure is predicted by theory to increase the achievable encoding accuracy of a neuronal population and may reflect a universal principle for population coding throughout the cortex.
Support Contributed By: MPI, NEI(NIH)},
department = {Department Logothetis},
talk_type = {Abstract Talk},
web_url = {http://www.sfn.org/absarchive/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Washington, DC, USA},
event_name = {35th Annual Meeting of the Society for Neuroscience (Neuroscience 2005)},
language = {en},
author = {Tolias, AS and Keliris, GA and Ecker, AS and Siapas, AG and Smirnakis, SM and Logothetis, NK}
}